You can see that the tvg-name tag is "Comedy Central US". Most of the US channels have "US" at the end of the tvg-id name. I would like to be able to remove the US from the name, since I know I am in the US.

The Channel name in your m3u file is the name at the very end of that line, because that's what we get from your IPTV provider.

In this case
group-title="USA ENTERTAINMENT",Comedy Central

Everything else in your new m3u file is added by us.

You can rename your channels in the editor, just click on the text field holding your channel name.
That should be obvious for any internet and computer user, given the fact that your mouse cursor changes to a text cursor and you can write into that field.

The tvg-name is used only by Perfect Player and it is needed for finding the right EPG for that channel.

It isn't even the displayed name in Perfect Player. Perfect Player (as most of the other apps too) shows the name placed at the very end of your line.

If you don't use Perfect Player, the tvg-name is totally irrelevant to you, so it absolutely doesn't matter what it is.